Vented shaped charge case



June 27, 1967 w T. BELL 3,32

VENTED SHAPED CHARGE CASE Filed March 8, 1966 I BY z Arro/r/v UnitedStates Patent O 3,327,630 VENTED SHAPED CHARGE CASE William T. Bell,Houston, Tex., assignor to Schlumberger Technology Corporation, Houston,Tex., a corporation of Texas Filed Mar. 8, 1966, Ser. No. 532,605 12Claims. (Cl. 10224) ABSTRACT OF THE DISCLOSURE This disclosure describesvarious means by which gases that may have entered a fluidly sealed butgas-pervious shaped charge container can be safely vented therefromwithout danger should the shaped charge be returned to the surfacewithout being detonated.

Accordingly, as will subsequently become apparent, this inventionrelates to shaped charges; and, more particularly, to means for safelyrelieving hazardous accumulations of gases under pressure from withinunfired encapsulated shaped charges as they are being removed from awell bore.

One of the most commonly used perforating devices employed today forperforating wells is the so-called encapsulated shaped charge. Suchencapsulated shaped charges are typically comprised of a hollowcontainer in which a shaped explosive and liner are mounted, with acover fluidly sealing the forward end of the container. The charges arecustomarily linked together as shown in Patent No. 3,100,443 or mountedeither on a so-cal led strip carrier (such as described in Patent No.3,048,101) or between a spaced pair of fairly stiff, but somewhatflexible, support members (such as those in Patent No. 3,282,213). Oncethey are mounted and all connections made, the shaped charges arelowered into a well bore from an electrical cable and positionedadjacent to a particular interval of formations. Then, once they arecalculated to be correctly positioned, the shaped charges are detonatedto produce the desired perforations through the casing and cement sheaththerearound.

Cast aluminum is one of the more popular materials used for fabricatingsuch shaped charge cases since it is easily machined and less expensivethan most other materials as well as leaves only minimum amounts ofdebris in a well upon detonation of the charges. Those skilled in theart do appreciate, however, that most cast aluminum alloys are more orless gas-pervious. Thus, as an aluminum shaped charge case is loweredeither into a ga-filled well bore or into one containing liquids withgases in solution, the high well bore pressures will slowly force gasesthrough the walls of the case which, of course, is initially atatmospheric pressure.

This accumulation of gases normally poses no particular problem so longas the shaped charge is detonated in the usual manner. It is not toouncommon, however, for some malfunction, as for example a defect in thedetonating system, to prevent detonation of one or more of the shapedcharges. It will be appreciated, however, that although the exteriorambient pressure in a well with liquid decreases as the unfired shapedcharges are withdrawn from a well bore, the gases filling the interiorof the cases will not escape as readily as they entered. Since time doesnot usually permit the unfired charges to be removed as slowly as theyWere lowered into a well, the interior of the cases will instead usuallyremain at a fairly high pressure that may be in the order of severalhundreds or even thousands of pounds/square inch as the shaped chargesare raised. Thus, as the shaped charges near the surface, it is not atall uncommon for the pressure differential from their interiors to theexterior to become sufliciently high to displace the cover of the casesat least partially, if not entirely, off of the containers.

Where the perforating apparatus must be withdrawn through narrowconfines, such as a small tubing string or a seating nipple, one or morecovers may have been displaced sufficiently to prevent the furtherpassage of the apparatus. In addition to many other obviousdisadvantages, such an occurrence, of course, requires a time-consumingfishing operation which, if unsuccessful, could necessitate theabandonment of a substantial portion of the perforating apparatus in thewell Ibore. This, is, of course, neither desired nor wanted. Similarly,even if the gas-filled shaped charges are eventually recovered with thecaps in place, they still present an obvious hazard to those conductingthe operation.

Where a perforating operation is conducted in a gas well under pressure,the upper end of the production tubing is typically capped with aso-called lubricator assembly which includes an exposed upright pipehaving a pressure-sealing gland at its upper end adapted to tightly sealaround a suspension cable and suitable valving 'at its lower end topermit the introduction and removal of cable-suspended tools into andout of the well. Thus, when perforating apparatus is being removed fromsuch a well with live charges, the apparatus is first pulled up into thelubricator and the valves therebelow closed.

It is, of course, then necessary to bleed-oh the gas pressure in thelubricator before the perforating apparatus can be removed.

In such instances, to save time, the lubricator pressure must bebled-off more rapidly than could possibly be afforded to decompress theunfired shaped charges. Thus, the pressure exterior of the unfiredshaped charges will be reduced much faster than the accumulated gasescan possibly permeate back through the aluminum cases. This rapiddepressuring will usually cause one or more of the caps to be displacedas far as the clearance between the shaped charges and internal wall ofthe lubricator will permit. The obvious hazard of removing a tightlystuck perforator with live charges and detonators from a lubricatorneeds no description to be fully appreciated.

Accordingly, it is an object of the present invention to provide meansfor releasing accumulated gases at high pressure from withinencapsulated shaped charges as they are being withdrawn from a wellbore.

This and other objects of the present invention are obtained byproviding a hollow shaped charge case formed of gas-pervious materialwith means that are selectively operable for venting accumulated gasesfrom within the case whenever the differential between the interiorpressure and the ambient pressure exterior of the case is sufiicient toactuate the venting means. In one manner of accomplishing this, anotherwise conventional shaped charge case is provided with venting meansfor releasing accumulated gases from within the case should it benecessary to retrieve the shaped charge from a Well bore beforedetonating it. The venting means include one or more passages throughthe case and sealing means that fluidly seal the passages againstentrance of fluids into the case but which open in response to a higherpressure within the case to release any accumulated gases therefrom.

The novel features of the present invention are set forth withparticularity in the appended claims. The present invention, both as toits organization and manner of operation together with further objectsand advantages thereof, may best be understood by way of illustrationand example of certain embodiments when taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a partially cross-sectioned view of a shaped charge enclosedwithin a case of a gas-pervious material and arranged in accordance withthe present invention;

FIG. 2 is a plan view of the forward end of the container shown in FIG.1;

FIG. 3 is a plan view similar to FIG. 2, but showing an alternateembodiment of a container arranged in accordance with the presentinvention; and

FIG. 4 is a partially cross-sectioned view similar to FIG. 1, butshowing still another embodiment of the present invention.

Turning now to FIG. 1, in one embodiment of the present invention, anencapsulated shaped charge 11) is shown comprised of a two-part case 11of a gas-pervious material, such as aluminum or the like, and having adished cover 12 snugly fitted over the forward portion 13 of a generallycylindrical hollow container 14 in which a preformed explosive pellet 15is disposed. To secure the cover 12 and container 14 together, the coveris counterbored, at 16, for receiving the forward portion 13 of thecontainer. By suitably dimensioning the mating portions to provide, forexample, an interference fit, the

cover 12 and container 14 will be snugly fitted together. i

As is typical, the forward end of the explosive pellet 15 is formed in agenerally conical, forwardly diverging, coaxial hollow that receives acomplementarily shaped metal liner 17. A booster explosive 18 isreceived within a shallow axial recess 19 formed in the internal surfaceof the rear wall 20 of the container 14. A spaced pair of rearwardlyextending longitudinal lugs 21 are provided for securing a det-onatingcord 22 against the external surface of the rear Wall of the container14 immediately opposite to the booster explosive 18. One or more sets oflongitudinally spaced lateral lugs 23 and 24 are provided on oppositesides of the container 14 and spaced to the rear of a circumferentialflange 25 around the central portion of the container to define groovesfor receiving a support 26.

The case 11, which is otherwise conventional, is provided with ventingmeans 27 in accordance with the present invention. The venting means 27include a circumferential groove 28 defined by the forward face 29 ofthe container flange 25 and the rearward marginal face .30 of the cover12. Longitudinal grooves 31 are extended along the exterior surface ofthe forward container portion 13 from between the forward flange face 29to transverse notches 32 across the forward face 33 of the forwardcontainer portion.

Thus, it will be seen that although the cover 12 is tightly fitted overthe forward container portion 13, direct communicaiton is providedthrough the passages 31 and 32 between the interior of the case 11 andthe circumferential groove 28. By fitting resilient sealing means, suchas an O-ring 34, into the circumferential groove 28, it will beappreciated that a greater external fluid pressure will urge the O-ringtightly against the opposed faces 29 and as well as the longitudinalsurface therebetween. On the other hand, should there be a greaterinternal pressure within the case 11 than that outside, such a greaterinternal pressure will displace the O-ring 34 radially outwardly asufficient distance to bleed-off any trapped pressure.

If it is preferred, a rearwardly directed circumferential skirt 35 of areduced external diameter may be provided around the rear marginal face30 of the cover 12 so as to substantially cover the longitudinal grooves31 as shown in FIG. 1. It will be recognized, however, that even thoughthe circumferential skirt 35 is over the longitudinal grooves 31, therewill be slight annular clearance, as at 36, between the rearwardmostedge of the skirt and the forward face 29 of the container flange 25.

Turning now to FIG. 3, an alternate embodiment is shown of a container11' that is otherwise similar to that shown in FIGS. 1 and 2, with thesame reference numerals being used but with prime marks to designateequivalent portions. In this alternate embodiment, the longitudinalgrooves 31 may be substituted by flats 31' formed tangentially acrossthe exterior surface of the forward container portion 13 and meeting thetransverse slots 32. These flats 31', of course, will provide sufficientclearance between the mating surfaces of the cover (not shown) andcontainer 14'.

Turning now to FIG. 4, an alternate embodiment is shown of still anothershaped charge 10 that is otherwise similar to that shown in FIGS. 1-3,but with double prime marks denoting equivalent elements. In thisalternate embodirnent, however, the previously described passages, suchas the grooves 31 or flats 31 along the external surfaces of the forwardcontainer portions 13 and 13, are replaced by similarly arrangedpassages, such as flats or longitudinal grooves 31", in the internalmating surface of the cover 12". The shaped charge 10" is otherwise thesame as that in FIGS. l-3.

Accordingly, it will be appreciated that whenever one of the shapedcharges 10-16" as shown in FIGS. 1-4 is lowered into a well bore, theO-rings 34-34" will fluidly seal the passage means (31-32, 31-32 or31"-32") to prevent entrance of fluids from the well bore into theinterior of the shaped charge cases 11-11. As previously described, asthe shaped charges 10-10" are lowered into the well bore, gases can andwill gradually permeate through the permeable metal of the cases 11-11and slowly accumulate therein. The pressure of these gases will, ofcourse, be whatever the ambient fluid pressure is around the shapedcharges 10-10. Should the shaped charges 10-10 be detonated in theexpected manner, the presence of gases therein will not materiallyaffect the performance of the shaped charge.

Should it be necessary, however, to retrieve one of the shaped charges111-111" from a well bore containing liquid without its having beendetonated, the exterior ambient pressure around the shaped charge willdiminish as it is raised. Inasmuch as accumulated gases within theshaped charge cases 11-11 cannot readily escape, however, the pressuredifferential between the interior of the case and their exterior willgradually increase, Then, once this pressure differential has reached anamount sufficient to expand the O-rings 34-34", the O-ring will bedisplaced radially outwardly at least a distance sufiicient to uncoverthe outer end of the passage means (31-32, 31'32' or 31"-32") andrelease at least a portion of the accumulated gases.

This release may occur several times during the ascent of the shapedcharges 1(1-10. Thus, by the time that the shaped charges 10-10" havereached the surface, a suflicient quantity of these trapped gases willhave been vented from the interior of the cases 11-11" to prevent thedisplacement of the covers 12-12" relative to the containers 14-14".Similarly, where the well bore is filled with high pressure gases, asthe pressure in the aforementioned lubricator is relieved, the ventingmeans 27- 27" will have operated one or more times to releaseaccumulated gases from the cases 11-11".

Accordingly, it will be appreciated that the present invention hasprovided new and improved means for preventing entrapped gases within ashaped charge case from displacing the cover relative to the containerbefore the pressure differential between the interior and exterior of ashaped charge case has reached an excessive magnitude otherwisesuflficient to displace the cover relative to the container. In thismanner, by venting off any accumulated gases whenever the pressuredifferential reaches a magnitude less than that necessary to displacethe cover, a shaped charge may be safely withdrawn from a well bore withits cover still firmly in position.

While particular embodiments of the present invention have been shownand described, it is apparent that changes and modifications may be madewithout departing from this invention in its broader aspects; and,therefore, the aim in the appended claims is to cover all such changesand modifications as fall within the true spirit and scope of thisinvention.

What is claimed is:

1. Shaped charge apparatus comprising: a hollow case having at least aportion of a gas-pervious material; shaped charge means in said case;means sealingly enclosing said shaped charge means within said case; andventing means for releasing accumulated gases from within the enclosedinterior of said case whenever the pressure exterior of said case islower than that in said enclosed intrior.

2. The apparatus of claim 1 wherein said case includes a cover and acontainer adapted to be joined together and wherein said gas-ventingmeans include resilient sealing means fluidly sealing said cover andcontainer to one another at their junction.

3. The apparatus of claim 2 wherein said gas-venting means furtherinclude passage means between the interior of said case and saidjunction of said cover and container.

4. The apparatus of claim 1 wherein said case includes a container and acover having complementarily-fitting portions adapted to be joinedtogether along mating surfaces and each defining an opposed marginalsurface, and wherein said gas-venting means include resilient sealingmeans fluidly sealed between said marginal surfaces around saidcomplementarily-fitting portions.

5. The apparatus of claim 4 wherein said gas-venting means furtherinclude passage means between the interior of said case and the enclosedspace between said resilient sealing means and saidcomplementarily-fitting portions.

6. The apparatus of claim 5 wherein said passage means extend along amating surface of one of said complementarily-fitting portions.

7. The apparatus of claim 5 wherein said passage means extend along themating surface of said cover portion.

8. The apparatus of claim 5 wherein said passage means extend along themating surface of said container portion.

9. Shaped charge apparatus comprising: a hollow case adapted tosealingly enclose an explosive charge and including a cover and acontainer of a gas-pervious material, said container having a peripheralflange providing a forwardly-directed marginal surface and a cylindricalportion forward of said peripheral flange, said cover having arearwardly-directed marginal surface defining the entrance of acylindrical bore therein adapted to receive said forward containerportion, said forward container portion and cylindrical bore havingcomplementary mating surfaces adapted for snugly inter-fitting saidcover and container to one another; and passage means along one of saidmating surfaces adapted for providing communication between the interiorof said case and the space between said marginal surfaces when saidcover is fitted onto said container.

10. The apparatus of claim 9 wherein said cover and container are ofcast aluminum.

11. The apparaus of claim 9 further including shaped charge means insaid case; and resilient sealing means in said space and sealinglyengaged with each of said opposed surfaces exterior of said passagemeans.

12. The apparatus of claim 11 wherein said cover and container are ofcast aluminum.

References Cited UNITED STATES PATENTS 2,891,477 6/1959 Swanson 10220 X2,984,307 5/1961 Barnes 10220 X 3,040,659 6/1962 McCullough 102-20BENJAMIN A. BORCHELT, Primary Examiner. V. R. PENDEGRASS, AssistantExaminer.

1. SHAPED CHARGE APPARATUS COMPRISING: A HOLLOW CASE HAVING AT LEAST APORTION OF A GAS-PERVIOUS MATERIAL; SHAPED CHARGE MEANS IN SAID CASE;MEANS SEALINGLY ENCLOSING SAID SHAPED CHARGE MEANS WITHIN SAID CASE; ANDVENTING MEANS FOR RELEASING ACCUMULATED GASES FROM WITHIN THE ENCLOSEDINTERIOR OF SAID CASE WHENEVER THE PRESSURE EXTERIOR OF SAID CASE ISLOWER THAN THAT IN SAID ENCLOSED INTERIOR.